1. Field of the Invention
The present invention generally relates to structures subject to excessive wear due to high compression contact, such as shroud support assemblies installed in aircraft gas turbine engines and other turbomachinery. More particularly, this invention relates to an improved method for refurbishing a shroud support assembly in the high pressure turbine section of a gas turbine engine.
2. Description of the Related Art
High bypass turbofan engines have a large fan that compresses incoming air, which is delivered to the combustion chamber and to the turbine section in the rear of the engine to generate additional engine thrust. The turbine is contained within a case equipped with a shroud, such that the shroud circumscribes the turbine and is adjacent to the tips of the turbine blades. The extent to which the blades, shroud and surrounding shroud support structure can be manufactured to close tolerances to minimize losses between the shroud and turbine blade tips is complicated by manufacturing tolerances, different rates of thermal expansion, and dynamic effects. As such, wear is also inevitable, particularly between the shroud and shroud support. An example of the latter is a stage 1 high pressure turbine (HPT) shroud support section 10 represented in FIGS. 1 and 2. In this example, the lip 14 and face 16 located at the forward flange 12 of the shroud support section 10 is particularly susceptible to excessive wear due to high compression contact with the stage 1 HPT nozzle outer band aft surfaces (not shown). The excessively worn surfaces can result in a non-serviceable condition of the shroud support section 10.
Various approaches have been developed for refurbishing worn surfaces of a shroud support, including building up these surfaces by thermal spraying a chromium carbide, nickel-base alloy or Co—Mo—Cr—Si alloy, or by weld build-up such as with the cobalt-base L605 superalloy. These refurbishment approaches, though successful, do not provide a long-term solution to the wear and dimensional degradation of shroud supports, thus adversely impacting fit, form and functionality. Furthermore, high manufacturing cost and cycle time resulting from thermal spray, welding and machining operations result in delays in repair/overhaul engine shipment and ultimately customer dissatisfaction. As an alternative, commonly-assigned U.S. Pat. No. 6,398,103 to Hasz et al. discloses a technique by which a wear-resistant foil is brazed to a worn surface of a component. The foil is formed by thermal spraying a wear-resistant material on a support sheet. Suitable wear-resistant materials include chromium carbide materials and Co—Mo—Cr—Si alloys, such as the commercially-available TRIBALOY® T400 and T800 alloys.
Notwithstanding the above advancements, it would be desirable if methods were available for refurbishing shroud supports that were less complicated, less labor-intensive and less costly, yet still provided a long-term solution to the aforementioned wear and dimensional degradation problems.